The present invention relates to photographic color developing compositions that are stable to calcium ions, and to a method for their use. This invention is useful in the field of photography to provide color photographic images.
The basic processes for obtaining useful color images from exposed color photographic silver halide materials include several steps of photochemical processing such as color development, silver bleaching, silver halide fixing and water washing or dye image stabilizing using appropriate photochemical compositions.
Photographic color developing compositions are used to process color photographic materials such as color photographic films and papers to provide the desired dye images early in the photoprocessing method. Such compositions generally contain color developing agents, for example 4-amino-3-methyl-N-(2-methane sulfonamidoethyl)aniline, as reducing agents to react with suitable color forming couplers to form the desired dyes. U.S. Pat. No. 4,892,804 (Vincent et al) describes conventional color developing compositions that have found considerable commercial success in the photographic industry. Other known color developing compositions are described in U.S. Pat. No. 4,876,174 (Ishikawa et al), U.S. Pat. No. 5,354,646 (Kobayashi et al) and U.S. Pat. No. 5,660,974 (Marrese et al).
It is common practice to add a xe2x80x9creplenishingxe2x80x9d solution to the color developing composition in the processing machine in order to replace photochemicals that are depleted during reaction or carried away by the processed materials. Such replenishment insures uniform development and maximum stability of the color developing agent.
Color developing compositions are commonly supplied in three or more xe2x80x9cpartsxe2x80x9d (or solutions) that are mixed immediately before use. Multiple parts are often required in order to separate and preserve the chemical activity and solubility of components that may otherwise deteriorate or react with each other when they are stored together for long periods of time under alkaline conditions. For example, one part might include a color developing agent. Another part might contain agents to preserve the alkalinity of the mixed color developing composition. Still another part may include an optical brightener. Upon combination of all parts and water, a homogeneous color developing composition can usually be obtained for the working strength solution in the processing machine.
There is a desire in the industry to reduce the number of parts used to prepare color developing compositions, and particularly to prepare replenishing solutions. A wide range of compositions are described in the art or commercially available as xe2x80x9cready to usexe2x80x9d solutions, concentrates or dry formulations. Liquid concentrates have only to be diluted with water to provide a working strength solution. Dry formulations need only be dissolved in water. For example, EP-A-0 793,141 (Chugai Photo) describes a two-part color developing composition that can be supplied in either solid or liquid form.
It is generally known that the concentrations of various photochemicals used in a photographic processing bath must lie within certain narrow limits in order to provide optimal performance. The most important solvent for such photoprocessing is water. Most inorganic salts can be readily dissolved in water while the organic photochemicals in such processing baths usually have suitable solubility in water at the desired operating concentrations.
However, water is both an asset and a major problem of ready-to-use and some concentrated photographic compositions because of its presence in high quantity. As a result, the costs of manufacturing, transport and storage of such compositions is steadily growing. Normally, the user of photochemical compositions has water available in which individual photochemicals could be mixed or diluted, but this is usually not practical for a number of reasons. The exact composition of the photochemicals is not readily determined by a common user and manufacturers are not likely to readily provide their formulations for such a purpose. Moreover, even if the formulations are known, mixing mistakes may result in poor photoprocessing results.
For these reasons, there is a trend in the photographic industry to provide photoprocessing compositions (including color developing compositions) in concentrated form so that the manufacturer and user need not pay for use, transport or storage of large volumes of water, and to enable use of smaller containers. Moreover, there has been a desire in the industry to provide compositions that can be used right out of their containers without the need for mixing various components (thereby reducing mixing errors), such as in what are known as xe2x80x9cautomatic replenishingxe2x80x9d processors.
One concentrated form known in the art is a chemical paste or slurry, as described for example in EP-A-0 204,372 (Chemco) and EP-A-0 800,111 (Fuji Photo). These formulations have still other disadvantages, namely lack of homogeneity and slow dissolution rate of solid components.
Additional small volume, ready to use color developing compositions are described in U.S. Pat. No. 5,273,865 (Loiacono et al). These compositions are said to be free of bromides, hydroxylamines and benzyl alcohol, to include a polyol compound having 4 to 8 hydroxy groups, and to be useful for rapid access processing of photographic elements having high silver bromide emulsions only.
There was a need in the photographic industry for a single-part color developing composition that is homogeneous, concentrated and stable. Such an attractive photographic product is described and claimed in copending and commonly assigned U.S. Ser. No. 09/132,200 (filed Aug. 11, 1998 by Darmon et al). Such compositions include one or more metal ion sequestering agents, similar to those described in Research Disclosure publication 13410 (June 1975) and publication 20405 (April 1981). These metal ion sequestering agents are said to stabilize color developing compositions in the presence of heavy metal ions such as iron and copper ions. Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 121 West 19th Street, New York, N.Y. 10011).
However, it has been found that some color developing compositions, whether prepared from concentrates or not, are formulated using local water supplies that are high in calcium ion content. It is necessary to insure that color developing compositions are not adversely affected by the inordinate calcium ion content that may be evident in some locales. Thus, it is desired to insure that such compositions are stable from precipitates, especially calcium precipitates that may evident as scale or deposits on processing equipment.
This invention provides an advance in the art with a photographic color developing composition that, when in aqueous form, has a pH of from about 7 to about 13, and comprises:
a) at least 0.0005 mol/l of a color developing agent in free base form,
b) at least 0.0005 mol/l of an antioxidant for the color developing agent,
c) at least 0.0005 mol/l of a polyaminopolyphosphonic acid or a salt thereof having at least five phosphonic acid groups, and
d) at least 0.00005 mol/l of a diphosphonic acid or a salt thereof that is either:
a hydroxyalklidene diphosphonic acid or a salt thereof, or
morpholinomethanediphosphonic acid or a salt thereof.
Further, this invention includes a method for providing a color image comprising contacting a color photographic silver halide element with the photographic color developing composition described above. This color developing step in a photographic processing method can be followed by desilvering the color developed color photographic silver halide element, as well as any other useful photoprocessing steps known in the art.
The color developing composition of this invention offers a number of advantages over the color developing compositions currently available or known in the art. It is less susceptible to the formation of precipitates with calcium ion because of the presence of a combination of specific amounts to two specific types of polyphosphonic acids (or salts thereof). Each specific type of polyphosphonic acid alone fails to provide this advantage, and other combinations of known heavy metal ion sequestering agents also fail in this regard. Thus, only the specific materials described for this invention provide the necessary protection against the variable calcium ion concentration in water supplied throughout the world. In other words, the composition of the invention is stable upon storage and use despite the source of make-up water.